With the greater variety of components used on printed circuit boards (PCBs), smaller passive components and larger ICs with finer ball pitch dimensions, the demands on high quality solder joints to aid PCB assembly (PCBA) fabrication and rework have increased. Faulty solder joint has cost companies billions of dollars over the years. Many processes have been developed to reduce failure rate for wave solder systems. However, for point to point handheld soldering and rework applications, companies are relying on operators' skills to produce good solder joints with quality electrical connections. Regardless of how much training is provided to the operators of the soldering iron, without guidance during a soldering activity, the operators may make and repeat mistakes due to the fact that there are many factors that impact heat transfer by the soldering iron for forming a solder joint with good electrical connection. These factors include solder tip temperature, geometry of the solder tip, oxidation of the solder, human behavior, and the like.
Moreover, automatic (e.g., robotic) soldering is currently strictly an open-loop time based event, where a robot moves to the specific joint, the solder tip is automatically placed on the joint, solder is automatically applied, and a prescribed time later (determined by a specific software for the robot), the solder tip is automatically removed from the joint. This process is repeated until the robot's program is complete.
Heating of a soldering tip is typically performed by passing an (fixed) electric current from a power supply through a resistive heating element. However, different soldering applications require different heating temperatures. Since a single tip having a specific alloy is capable of producing heat at a certain (maximum) temperature, different soldering tips are needed for different heating applications. Simple soldering irons reach a temperature level determined by thermal equilibrium, dependent upon power (current) input and the materials of the workpiece, which it contacts with. However, the tip temperature drops when it contacts a large workpiece, for example, a large mass of metal and therefore a small soldering tip will lose significant temperature to solder a large workpiece. More advanced soldering irons have a mechanism with a temperature sensor to keep the tip temperature steady at a constant level by delivering more power to the tip, when its temperature drops.
Typically, a variable power control, which changes the equilibrium temperature of the tip without automatically measuring or regulating the temperature. Other systems use a thermostat, often inside the iron's tip, which automatically switches power on and off to the soldering cartridge/tip. A thermocouple sensor may be used to monitor the temperature of the tip and adjust power delivered to the heating element of the cartridge to maintain a desired constant temperature.
Another approach is to use magnetized soldering tips which lose their magnetic properties at a specific temperature (the Curie point). This approach depends on the electrical and metallurgical characteristics of a particular tip material. For example, the tip may include copper, which is a material with high electrical conductivity, and another magnetic material (metal) with high resistivity. As long as the soldering tip is magnetic, it closes a switch to the power supply and the heating element. When the temperature of the tip exceeds the required temperature (for the specific application), it opens the switch and thus the tip starts cooling until the temperature drops enough to restore magnetization of the tip material. The selection of a material with a fixed Currie point results in a heater that generates and maintain a specific, self-regulated temperature and the constant level and thus the heater requires no calibration. That is, when the heater temperature drops (when it contacts a thermal load), the power supply responds with sufficient power required to increase the tip temperature back to the fixed required temperature to correctly solder the workpiece. Again, a specific tip having a specific alloy with particular magnetization properties is capable of producing heat at or up to a certain temperature. Accordingly, different soldering tips are needed for different heating applications. This requires an inventory and maintenance of a variety of different soldering tips with different thermal characteristics. It also adds significant time to the soldering process of a workpiece large enough or with different types of components that require different tips since the operator has to keep changing the soldering tips.